Throughout this application, various publications are referenced in parentheses by author and year. Full citations for these references may be found at the end of the specification immediately preceding the claims. The disclosures of these publications in their entireties are hereby incorporated by reference into this application to describe more fully the art to which this invention pertains.
Normal bladder function requires coordinated bladder contraction and urethral sphincter relaxation during the emptying phase and the opposite, bladder relaxation and urethral sphincter contraction, during the filling/storage phase. The occurrence of irregularities in these processes increases with age in males and females and can lead to a variety of disorders of lower urinary tract function, including incontinence and urinary retention.
Incontinence and Urinary Retention
Incontinence is characterized by the involuntary loss of urine. It can be divided generally into two types, stress and urge incontinence. Stress incontinence is characterized by an inability to generate or maintain normal closing pressure at the bladder outlet and urethra. Involuntary urine loss can be provoked whenever the physical stress of everyday activities causes abdominal pressure to rise above the level of the bladder closing pressure; hence the name. The underlying pathology may involve (1) damage to the nerves which send contractile signals to these structures (such as may occur during childbirth), or (2) loss of mass of the urothelium after menopause, or (3) other processes which result in primary muscle weakness or loss of tone to these structures (Wein, 1987; Andersson, 1988).
Urge incontinence, in contrast, involves primarily changes in the function of the main body (detrusor) of the bladder. These changes disrupt the normal manner in which bladder volume/distention is sensed and translated into, first, the desire to void and, ultimately, the neuronal impulses signaling detrusor contraction. Rather than a graded response to bladder distention, patients with urge incontinence experience involuntary leakage preceded by a sensation of urgency and impending urinary loss. A large portion of patients with urge incontinence are shown by urodynamic evaluation to have detrusor instability, characterized by spontaneous, involuntary contractions (Swami and Abrams, 1996). The underlying pathology may involve either the sensory or motor nervous systems innervating the detrusor, or may be associated with inflammation and irritative processes in the bladder muscle, or may be idiopathic (Andersson, 1988).
As the name implies, urinary retention describes a condition in which there is difficulty in voiding. In some instances this may occur as a result of bladder outlet obstruction, as is seen in patients with benign prostatic hyperplasia (BPH). Indeed, chronic bladder outlet obstruction may lead to secondary bladder hyper-reflexia which may persist after correction of the obstruction and may involve remodeling of the neuronal circuitry of the bladder (Swami and Abrams, 1996). Urinary retention in the absence of bladder outlet obstruction may arise from deficits in the same systems as urge incontinence: the neurons or smooth muscle of the detrusor.
Neural Control of the Urinary Bladder
The contractile activity of the lower urinary tract structures is controlled primarily by two neurotransmitter systems (Wein, 1987). Neurons of the sympathetic nervous system innervate the urethra and bladder base, and to a lesser extent the detrusor, releasing the neurotransmitter norepinephrine (NE). The smooth muscle of the urethra and bladder base are endowed with alpha-adrenergic receptors where NE acts to cause contractions. In contrast, adrenergic receptors of the detrusor are of the beta-adrenergic subtype, the activation of which causes relaxation. Thus, activation of the sympathetic nervous system in the bladder promotes urine storage. Parasympathetic neurons innervate the detrusor, but not the bladder base or urethra. Parasympathetic neurons release the neurotransmitters acetylcholine (ACh) and adenosine-5xe2x80x2-triphosphate (ATP) which act, respectively, at M3-muscarinic and P2X-purinergic receptors to elicit contractions. Activation of the parasympathetic nervous system, therefore, promotes bladder emptying.
Although these neuronal systems play a key role in the motor activity of the lower urinary tract, other neurotransmitters are involved to varying degrees in different species, and possibly to varying degrees during different pathological states within a given species (e.g. humans). Indeed, Ferguson and Christopher (1996) state that xe2x80x9cup to 50% of contractile activity in patients with bladder instability is sensitive to tetrodotoxin (i.e., is of neuronal origin) but resistant to atropine, suggesting that purinergic (i.e., involving the neurotransmitter ATP) or other NANC (non-adrenergic, non-cholinergic) neurotransmission plays a greater role in pathological conditions.xe2x80x9d
In addition to transmitters stored in and released from terminals of efferent nerves, transmitters of afferent nerves and their receptors are also involved in the control of lower urinary tract function. Tachykinins, such as substance P, neurokinins A and B, and other neuropeptides have been demonstrated in nerves of the lower urinary tract and shown to be able to influence bladder function (Andersson, 1996). Among the xe2x80x98non-classicalxe2x80x99 transmitters which have been studied is nitric oxide, which plays a role in the relaxation of the bladder base and urethra during micturition (Werkstrom et al., 1997). One of the more extensively studied classical neurotransmitters in the bladder is 5-hydroxytryptamine (5-HT). In the human detrusor 5-HT has been shown to have multiple effects on bladder contractility. One of the ways in which 5-HT has been shown to affect contractions is by modifying the neuronal release of the primary parasympathetic neurotransmitters, ACh and ATP (see below).
Current Treatments for Micturition Disorders
A variety of pharmaceutical agents have been employed to treat micturition disorders. Drugs used to reduce bladder contractility associated with urge incontinence include muscarinic receptor antagonists, calcium channel blockers, direct smooth muscle relaxants, and beta-adrenergic receptor agonists (Andersson, 1988). In addition, prostaglandin synthesis inhibitors and tricylic antidepressants have been investigated for this purpose (Andersson, 1988). More recently, there has been an interest in developing potassium channel openers, aimed at reducing contractility by hyperpolarizing detrusor smooth muscle cells (Ohnmacht et al., 1996). The most commonly employed therapeutic agents for increasing bladder outlet resistance are the alpha-adrenergic receptor agonists and estrogen (Wein, 1987). The only agents which are effective at increasing detrusor contractions and improving bladder emptying are the muscarinic receptor agonists (Andersson, 1988). Each of these therapies is associated with limited efficacy and unwanted side effects (Andersson, 1988; Wein, 1987).
5-HT in Bladder Function
The physiological role of 5-hydroxytryptamine (5-HT) in bladder detrusor varies widely among different species, with respect to both the nature of response and the receptor subtype involved. For example, 5-HT produces marked contractions mediated by postjunctional 5-HT2 receptors in isolated detrusor from cat (Saxena et al., 1985) and dog (Cohen, 1990). Potent direct 5-HT-evoked contractions have also been described for human detrusor strips (Klarskov and Hxc3x8rby-Petersen, 1986). Although the responses were found to be relatively insensitive to 0.1 xcexcM ketanserin, and therefore not associated with 5-HT2A receptor activation, the identity of the subtype involved remains to be determined. In contrast, direct contractile effects of 5-HT are absent in the bladder body of rat and guinea pig (Cohen and Drey, 1989) and monkey (Waikar et al., 1994). Unlike other species, the monkey bladder expresses postjunctional 5-HT4 receptors, activation of which produces relaxation (Waikar et al., 1994).
In addition to these direct effects, 5-HT receptors play a role in modulating the contractile effects of neuronally released ACh and ATP. Thus, it has been reported that 5-HT in the mouse urinary bladder enhances electrically evoked, neuronally mediated contractions via activation of 5-HT1B (Holt et al., 1985, 1986; Cleal et al., 1989) and ketanserin-sensitive 5-HT2 (Cleal et al., 1989) receptors located prejunctionally. In guinea pig detrusor, activation of prejunctional 5-HT4 and 5-HT2A receptors leads primarily to an increase in purinergic activity (Messori et al., 1995), while 5-HT-evoked increases in cholinergic activity in guinea pig (Messori et al., 1995), rabbit (Chen, 1990), and cat (Saxena et al., 1985) are mediated by 5-HT3 receptors. In addition to 5-HT3 receptors, 5-HT4 subtypes have been shown to mediate the potentiation of cholinergic, neuronally induced contractions of isolated human detrusor (Corsi et al., 1991; Tonini et al., 1994). Furthermore, Corsi et al. (1991) also described the opposite effect, i.e. inhibition of cholinergic responses induced by micromolar concentrations of 5-HT, and ascribed these to activation of 5-HT1-like receptors.
Discovery of 5-HT7 and 5-HT2B Receptor Function in the Urinary Bladder
The investigations leading to the present invention were inspired by our finding that messenger RNA for the 5-HT7 receptor is present in tissue specimens from human (Bard et al., DNA Encoding a Human Serotonin Receptor (5-HT4B) And Uses Thereof, U.S. patent application Ser. No. 08/281,526, now U.S. Pat. No. 6,083,749, issued Jul. 4, 2000) and rat urinary bladders (see below), as well as the localization of the 5-HT2B receptor in the rat bladder (see below; PCT International Application Nos. WO 95/24200, WO 97/35578). The xe2x80x9c5-HT7 receptorxe2x80x9d had previously been known as the xe2x80x9c5-HT4B receptorxe2x80x9d until it was renamed by the Serotonin Receptor Nomenclature Committee of the IUPHAR (Hoyer et al., 1994). Prior to our investigation, the role of 5-HT in contractile activity of the rat bladder, as opposed to other species (see above) was considered to be insignificant (Cohen and Drey, 1989). In order to ascertain the physiological role of the rat bladder 5-HT7 and 5-HT2B receptors, we explored the possibility that these receptors may modulate the activity of the parasympathetic nervous system in the bladder. To simulate this condition, we employed an electrical stimulus of sufficient intensity to activate only the intrinsic detrusor neurons. Prior to this study, the effects of 5-HT in electrically stimulated preparations of rat bladder have not been described.
This invention relates to the discovery that activation of 5-HT7 receptors in the bladder leads to an increase in the magnitude of contractions mediated by neurotransmitters of the parasympathetic nervous system. In the course of our investigations, we discovered unexpectedly that the 5-HT2B receptor subserves the same role in the bladder: i.e., activation of the 5-HT2B receptor also leads to an increase in the magnitude of contractions mediated by parasympathetic neurotransmitters. Thus, this document is the first describing the presence and functional role of the 5-HT7 receptor in the bladder, the first to describe a role of the 5-HT7 receptor in which activation of the receptor causes augmentation of neuronal activity in any physiological system in any species, and the first to describe the functional role of the 5-HT2B receptor in the bladder. Hence, the possibility that agents acting at either (a) the 5-HT7 receptor alone, or (b) the 5-HT7 and 5-HT2B receptors in combination may be of value in the treatment of micturition disorders was heretofore unrecognized by those skilled in the art. Because of the key role of parasympathetic neurotransmitters in the control of bladder function, it is proposed that compounds which activate 5-HT7 receptors, or both 5-HT7 and 5-HT2B receptors, will be useful in treating urinary retention, by virtue of their ability to facilitate muscular contractions, thereby promoting more efficient elimination of urine. Conversely, compounds which act to antagonize the actions of 5-HT at 5-HT7 receptors or both 5-HT7 and 5-HT2B receptors, will be useful in treating urinary urge incontinence, by acting to diminish the neurogenic impulses which initiate detrusor contraction.
The present invention provides a method of treating urinary incontinence in a subject which comprises administering to the subject a therapeutically effective amount of either a 5-HT7 receptor antagonist or an antagonist that acts at both 5-HT7 and 5-HT2B receptors to reduce abnormal neurogenically mediated contraction of the urinary bladder. The invention also provides a method of treating urinary retention in a subject which comprises administering to the subject a therapeutically effective amount of either a 5-HT7 receptor agonist or an agonist that acts at both 5-HT7 and 5-HT2B receptors to increase contraction of the urinary bladder.
The invention provides a method of treating urinary incontinence in a subject which comprises administering to the subject a therapeutically effective amount of a 5-HT7 antagonist which binds to the human 5-HT7 receptor with an affinity at least ten-fold higher than the affinity with which it binds to each of the human 5-HT1A, 5-HT2A, 5-HT2C, 5-HT3, 5-HT4, and 5-HT6 receptors.
Preferably, the aforementioned 5-HT7 antagonist additionally binds to the human 5-HT7 receptor with an affinity at least ten-fold higher than the affinity with which it binds to each of the human 5-HT1B, 5-HT1D, 5-HT1E, 5-HT1F, 5-HT5A, and 5-HT5B receptors.
In an additional embodiment of the invention, the 5-HT7 antagonist is also a 5-HT2B antagonist which binds to the human 5-HT2B receptor with an affinity at least 10-fold higher than the affinity with which it binds to each of the human 5-HT1A, 5-HT2A, 5-HT2C, 5-HT3, 5-HT4, and 5 -HT6 receptors.
Preferably, the 5-HT7 antagonist additionally binds to the human 5-HT2B receptor with an affinity at least ten-fold higher than the affinity with which it binds to each of the human 5-HT1B, 5-HT1D, 5-HT1E, 5-HT1F, 5-HT5A, and 5-HT5B receptors.
The invention also provides a method of treating urinary retention in a subject which comprises administering to the subject a therapeutically effective amount of a 5-HT7 agonist which activates the human 5-HT7 receptor at least ten-fold more than it activates each of the human 5-HT1A, 5-HT2A, 5-HT2C, 5-HT3, 5-HT4, and 5-HT6 receptors.
Preferably, the aforementioned 5-HT7 agonist additionally activates the human 5-HT7 receptor at least ten-fold more than it activates each of the human 5-HT1B, 5-HT1D, 5-HT1E, 5-HT1F, 5-HT5A, and 5-HT5B receptors.
In an additional embodiment of the invention, the 5-HT7 agonist is also a 5-HT2B agonist which activates the human 5-HT2B receptor at least ten-fold more than it activates each of the human 5-HT1A, 5-HT2A, 5-HT2C, 5-HT3, 5-HT4, and 5-HT6 receptors.
Preferably, the 5-HT7 agonist additionally activates the human 5-HT2B receptor at least ten-fold more than it activates each of the human 5-HT1B, 5-HT1D, 5-HT1E, 5-HT1F, 5-HT5A, and 5-HT5B receptors.
The invention further provides a method of treating urinary incontinence in a subject which comprises administering to the subject a therapeutically effective amount of an admixture of a 5-HT7 antagonist and a 5-HT2B antagonist, wherein both the affinity with which the 5-HT7 antagonist binds to the human 5-HT7 receptor and the affinity with which the 5-HT2B antagonist binds to the human 5-HT2B receptor are at least ten-fold higher than the affinity with which each antagonist binds to each of the human 5-HT1A, 5-HT2A, 5-HT2C, 5-HT3, 5-HT4, and 5-HT6 receptors.
Preferably, the 5-HT7 antagonist additionally binds to the human 5-HT7 receptor and the 5-HT2B antagonist additionally binds to the human 5-HT2B receptor with an affinity at least ten-fold higher than the affinity with which each antagonist binds to each of the human 5-HT1B, 5-HT1D, 5-HT1E, 5-HT1F, 5-HT3A, and 5-HT5B receptors.
The invention also provides a method of treating urinary retention in a subject which comprises administering to the subject a therapeutically effective amount of an admixture of a 5-HT7 agonist and a 5-HT2B agonist, wherein both the 5-HT7 agonist activates the human 5-HT7 receptor and the 5-HT2B agonist activates the human 5-HT2B receptor at least ten-fold more than the extent to which each agonist activates each of the human 5-HT1A, 5-HT2A, 5-HT2C, 5-HT3, 5-HT4, and 5-HT6 receptors.
Preferably, the 5-HT7 agonist additionally activates the human 5-HT7 receptor and the 5-HT2B agonist additionally activates the human 5-HT2, receptor at least ten-fold more than the extent to which each agonist activates each of the human 5-HT1B, 5-HT1D, 5-HT1E, 5-HT1F, 5-HT5A, and 5-HT5B receptors.
In addition, the invention provides a process for making a composition of matter which specifically binds to a human 5-HT7 receptor which comprises identifying a chemical compound using any of the processes described herein for identifying a compound which binds to and/or activates or inhibits activation of a human 5-HT7 receptor and then synthesizing the chemical compound or a novel structural or functional analog or homolog thereof.
This invention further provides a process for preparing a pharmaceutical composition which comprises admixing a pharmaceutically acceptable carrier and a pharmaceutically acceptable amount of a chemical compound identified by any of the processes described herein for identifying a compound which binds to and/or activates or inhibits activation of a human 5-HT7 receptor or a novel structural or functional analog or homolog thereof.
The invention also provides a process for making a composition of matter which specifically binds to human 5-HT7 and 5-HT2B receptors which comprises identifying a chemical compound using any of the processes described herein for identifying a compound which binds to and /or activates or inhibits activation of human 5-HT7 and 5-HT2B receptors and then synthesizing the chemical compound or a novel structural or functional analog or homolog thereof.
This invention further provides a process for preparing a pharmaceutical composition which comprises admixing a pharmaceutically acceptable carrier and a pharmaceutically acceptable amount of a chemical compound identified by any of the processes described herein for identifying a compound which binds to and/or activates or inhibits activation of human 5-HT7 and 5-HT2B receptors or a novel structural or functional analog or homolog thereof.